The present invention is related generally to toner cartridges for imaging devices and, more particularly, to the reduction or elimination of toner leakage from such devices.
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices, such as laser printers and copiers, use toner particles to form the desired image on the print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller that is engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure.
FIG. 1 is a diagram of typical laser printing device 100 employing an Electrophotography (EP) process. For monochromatic printing, a single color of toner particles 101 is held in toner supply hopper 102. Toner particles 101 are typically small plastic (e.g., styrene) particles on the order of 5 microns (10xe2x88x926 meter) in size. Agitator (or stirring blade) 103 is typically made of plastic such as mylar and ensures toner particles 101 are uniformly positioned along developer sleeve 104 while inducing a negative charge onto the toner particles in the range of xe2x88x9230 to xe2x88x9280 micro coulomb per gram (xcexcc/g). Developer sleeve 104 rotates in a counterclockwise direction about an internal stationary magnet 105 acting as a shaft. Toner particles 101 are attracted to the rotating developer sleeve 104 by the magnetic forces of stationary magnet 105. Doctor blade 106 charges the toner and metes out a precise and uniform amount of toner particles 101 onto developer sleeve 104 as its outer surface rotates external to toner supply hopper 102. Developer sealing blade 107 removes excess toner particles 101 affixed to developer sleeve 104 as its outer surface rotates back into toner supply hopper 102. Developer sealing blade 107 removes excess toner particles 101 affixed to developer sleeve 104 as its outer surface rotates back into toner supply hopper 102 and prevents toner particles 101 from falling out of toner supply hopper 102 onto paper, along the length of developer sleeve 104.
Primary Charging Roller (PCR) 108 conditions Organic Photo Conductor (OPC) drum 109 using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum 109. Production of the uniform charge by PCR 108 also has the effect of erasing residual charges left from any previous printing or transfer cycle.
A critical component of the EP process is OPC drum 109. OPC drum 109 is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PCR 108. Initially, the unexposed surface potential of the OPC is charged to approximately xe2x88x92600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the underlying aluminum substrate.
Scanning laser beam 110 exposes OPC drum 109 one line at a time at the precise locations that are to receive toner (paper locations which correspond to dark areas of the image being printed). OPC drum 109 is discharged from xe2x88x92600V to approximately xe2x88x92100V at points of exposure to laser beam 110, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles 101 are magnetically attracted to rotating developer sleeve 104. Alternatively, if a nonmagnetic toner is used, developer sleeve 104 may comprise a developer roller to mechanically capture and transport toner particles 101. In this case, an open cell foam roller may be included to apply toner to developer sleeve 104. The still negatively charged toner particles held by developer sleeve 104 are attracted to the relatively positively charged areas of the surface of OPC drum 109 and xe2x80x9cjumpxe2x80x9d across a small gap to the relatively positively charged latent image on OPC drum 109 creating a xe2x80x9cdevelopedxe2x80x9d image on the drum.
Paper to receive toner from OPC drum 109 is transported along paper path 111 between OPC drum 109 and transfer roller 112, with the developed image transferred from the surface of OPC drum 109 to the paper. The transfer occurs by action of transfer roller 112 which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles and causing them to move onto the paper. Wiper blade 113 cleans the surface of the OPC drum 109 by scraping off the waste (untransferred) toner into waste hopper 115, while recovery blade 114 prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller 116 and pressure roller 117 where the toner is melted and fused (or xe2x80x9cbondedxe2x80x9d) to the paper. Heated roller 116 and pressure roller 117 are together referred to as the fuser assembly.
One design consideration with EP imaging devices, such as laser printers, is to minimize the leakage of toner from the hopper. Leakage sometimes occurs at the ends of developer sleeve 104. Several methodologies and arrangements have been used to reduce or eliminate toner leakage from the ends of developer sleeve 104. Some printers employ a foam or felt mechanical seal at the ends of developer sleeve 104 as a physical barrier to prevent toner particles from slipping past the interface between developer sleeve 104 and toner supply hopper 102. Alternatively, when the toner includes magnetic properties, such as in many black and white printers, magnetic seals may be provided at the ends of developer sleeve 104 to tract monochromatic toner particles and create a physical barrier, consisting of the monochromatic toner particles, to prevent additional particles from leaking. Unfortunately such techniques are generally inapplicable to the non-magnetic type of toner used, for example, in most color printers and copiers.
FIG. 2 shows developer roller 201 with conventional prior art seal 202 in place to reduce toner leakage. Seal 202 rides along an outer surface of developer roller 201. However, toner fluid pressure may be sufficient to cause toner particles to seep under seal 202 and out the end of the roller assembly.
Accordingly, a need exists for a structure and method for reducing toner leakage in a torner cartridge.
The present invention is directed to a sealing mechanism for use in a toner cartridge comprising a developer roller with an annular groove. In one embodiment of the invention, the annular groove intrudes into the surface, a bottom of the groove having a diameter smaller than a diameter of the outer roller. A flexible end seal has a stepped profile, a central portion extending into and engaging the annular groove and peripheral outer portion in contact with an outer surface of the roller.